scitechcox - Modulation

Introduction:

Radio stations work with two waves, known as carrier waves and signal waves. Carrier waves are assigned to the station by the FCC, and remain constant. These are the waves that make each station different, and these are the frequencies that your radio tuner needs to match for you to listen to that station. These frequencies are well above the range of human hearing, with AM around 1 million vibrations per second (Hz) and FM around 100 million vibrations per second (Hz).

Activity:

When the station has information they want to send over the carrier waves, they use a signal wave. The signal wave is the information that gets broadcast. The signal wave would come from the announcers voice, or the music played by the DJ. This signal wave has to change, or modulate, the carrier wave. As the signal wave changes, the carrier wave gets changed along with it. How does the carrier wave get changed? It depends on whether you are listening to AM or FM.
- AM signals start with a defined carrier wave, and change or Modulate the Amplitude (hence, AM). The wave looks just like the carrier wave, but with bulges that outline the signal wave.
- FM signals start with a defined carrier wave, and change of Modulate that Frequency (hence, FM). The wave looks just like the carrier wave, but stretched or compressed in the pattern of the signal wave.